Ejection of Molten Tin Droplets in the Presence of a Hydrogen Plasma

One of the significant obstacles left if the development of a fusion power plant is the development of Plasma Facing Components (PFCs) that can withstand the large heat and particle flux incident on the first wall and divertor region. As solid PFCs struggle with microstructure growth, sputtering and melting, liquid metals have been a popular potential replacement. Liquid metal’s use as a PFC has been increasing due to its ability to self-repair damage as well as pump lost fuel and waste particles to create a low recycling edge. Currently, tin, lithium and lithium eutectics are the commonly considered liquid metals for use as a fusion PFC. It is therefore important to research the Plasma Material Interaction (PMI) between a hydrogen plasma and the liquid metal PFC candidates. This work, conducted at the Center for Plasma Material Interaction (CPMI), investigated how a molten tin surface reacts when exposed to a hydrogen plasma, building off observations by ASML of particles being ejected from a molten tin surface in the presence of a hydrogen plasma. For this work molten tin was exposed to a hydrogen plasma, of varying electron densities and temperatures, and any ejected particles were collected on a witness plate to determine the particle sizes, angular distribution and mass flux. This work found the ejected tin particles range in size from 10’s of nm<!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'> nms to 10’s of microns and that the mass flux of tin from the molten surface is in the 10’s of mg/(m² s)The work done shows macroscopic amounts of molten tin are ejected in the presence of a hydrogen plasma, making tin not suitable as a fusion PFC.